In electrochemical cells using current flow through a diaphragm in the cell, holes in the diaphragm are indicated by increase in the concentration of hypochlorite in the vicinity of the cathode. An apparatus for measuring hypochlorite concentration in the catholyte is described in copending application Ser. No. 762,225 of the common assignee of the present disclosure. Such a measurement system utilizes a pair of dissimilar metal electrodes, the preferred embodiment utilizes a platinum electrode whch is exposed to the hypochlorite in the catholyte. The catholyte solution is strongly basic, (usually NaOH), and the electrode thus ultimately forms a film over the surface as a result of exposure to the strong basic catholyte. The preferred electrode material is platinum but it will be understood that other noble metals can also be used.
The procedure of the present disclosure sets forth a method of cleaning the exposed electrode. Even though the electrode is a noble metal that does not easily oxidize, it does nevertheless on exposure to strong basic catholyte form a surface film which might be described as an oxidation film. Ultimately, this film interferes with the function of the electrode. This is especially important because the sensitivity of the measurement system depends in large part on having clean electrode surfaces, meaning surfaces free of film or other deposits thereon.
The present procedure cleans such a surface, and particularly restores the surface to a bright metal condition substantially free of surface film. The procedure is successful with noble metals other then platinum including gold and silver. It is particularly able to cleanse electrodes which have been exposed to strong basic solutions forming the film on the electrodes. It is believed to be successful for electrodes of any shape provided they can be exposed to the process described below and connected in a circuit as will be described.
One reference of interest is U.S. Pat. No. 3,030,286. This is directed to descalling titanium alloy articles. U.S. Pat. No. RE28,849 is a surface preparation process utilizing various strong acids. U.S. Pat. No. 3,574,074 discloses an AC current system using a strong acid. As will be more readily apparent upon consideration of the specification below, there are a number of factors wherein the hypochlorite measuring electrodes of the present disclosure are dressed and prepared for accuracy or repetition in operation by the treatment herein disclosed. References is made to the specification and the drawings described below.